Monolithic, electrically small, multi-frequency antenna

ABSTRACT

A projectile having a telemetry system built in which requires an antenna which is structurally incorporated into the nose cone of the projectile. A dielectric material shaped to conform to the nose cone of the projectile is adapted to be part of the projectile exterior wall structure. A thin metallic coating is deposited on the entire inside surface of the dielectric nose cone and the coating is extended to cover a portion of the outside surface such as to leave the tip of the nose cone exposed, thereby defining an open end dielectric loaded radiator. A slot shaped aperture is provided in the coating and is located at the base of the nose cone so as to expose a portion of the dielectric and thereby define a slotted dielectric loaded cavity. A plurality of metallic coated holes are located circumferentially around the nose cone so as to electrically separate the open ended dielectric loaded radiator from the slotted dielectric loaded cavity. The resultant product is a multi-frequency, monolithic conical dielectric loaded cavity antenna.

United States Patent [1 1 Jones, Jr.

[ Oct. 21, 1975 MONOLITHIC, ELECTRICALLY SMALL,

MULTl-FREQUENCY ANTENNA [75] lnventorz' Howard S. Jones, Jr.,Washington,

[73] Assignee: The United States of America as represented by theSecretary of the Army, Washington, DC.

22 Filed: June 11, 1974 21] Appl. No: 478,204

[52] U.S. Cl. 343/708; 343/725; 343/769; 343/785 [51] Int. Cl. H01Q 1/28[58] Field of Search 343/708, 725, 769, 770, 343/785 [56] ReferencesCited UNITED STATES PATENTS 3,798,653 3/1974 Jones 343/708 PrimaryExaminerEli Lieberman Attorney, Agent, or FirmNathan Edelberg; Robert P.Gibson; Saul Elbaum [57] ABSTRACT A projectile having a telemetry systembuilt in which requires an antenna which is structurally incorporatedinto the nose cone of the projectile. A dielectric material shaped toconform to the nose cone of the projectile is adapted to be part of theprojectile exterior wall structure. A thin metallic coating is depositedon the entire inside surface of the dielectric nose cone and the coatingis extended to cover a portion of the outside surface such as to leavethe tip of the nose cone exposed, thereby defining an open enddielectric loaded radiator. A slot shaped aperture is provided in thecoating and is located at the base of the nose cone so as to expose aportion of the dielectric and thereby define a slotted dielectric loadedcavity. A plurality of metallic coated holes are locatedcircumferentially around the nose cone so as to electrically separatethe open ended dielectric loaded radiator from the slotted dielectricloaded cavity. The resultant product is a multi-frequency, monolithicconical dielectric loaded cavity antenna.

4 Claims, 4 Drawing Figures US. Patent Oct. 21, 1975 Sheet10f2 3,914,767

US. Patent Oct. 21, 1975 Sheet 2 of2 3,914,767

MONOLITHIC, ELECTRICALLY SMALL, MULTI-FREQUENCY ANTENNA The inventiondescribed herein may be manufactured, used and licensed by or for thegovernment for governmental purposes without the payment to the inventorof any royalties thereon.

BACKGROUND OF THE INVENTION Since the advent of projectiles utilizingproximity fuzing systems, telemetry, missile guidance, and other typesof electronic communications, a problem in the design of such systemshas been to provide an antenna which is small, compact and will not takeup too much space within the projectile. This is especially importantwhere the projectile has a fixed size and where space and weightlimitations are critical problems in the design of self-contained fuzingand telemetry systems. Another problem has been to construct antennas insmall diameter bodies which can handle signals at the lower microwavefrequencies (800 to 2,500 mHz.) and which would lend themselves tomulti-elements construction. It is also important that the electricalcharacteristics of these antennas meet design specifications. Thisnormally means that the antenna must have certain specified radiationpattern characteristics, impedance matching and sufficient bandwidth andgain to fulfill the telemetry function.

Prior systems have utilized small antennas which are usually mounted inthe nose structure of the projectile. These antennas used in priorsystems normally utilized radiation elements such as loops, stubs andring networks that were enclosed by the dielectric nose cone or body ofthe projectile. These elements have proven to be less efficient and moredifficult to design and construct, and also far more costly to producethan is desirable for such systems. While many of the electricalcharacteristics desired could have been obtained with the use of cavitywave guide antennas, these antennas could not be used because of theirextremely large size and heavy weight which has been inherent in thedesign of such systems. It is, therefore, an object of this invention toprovide a projectile with an antenna system that uses a minimum of spacewithin the projectile.

It is another object of this invention to provide a small, compactantenna system for a projectile which is efficient in its electricalcharacteristics and yet is extremely lightweight.

Still another object of the invention is to provide an antenna for aprojectile which can be incorporated as part of the nose cone structureof the projectile.

Yet another object of the invention is to provide an antenna system forprojectiles which can be easily constructed and is inexpensive tomanufacture.

An additional object of the invention is to provide a new and uniqueantenna design having low input impedance and good bandwidth.

A further object of this invention is to provide an antenna designhaving multi-frequency design capabilities with good electricalisolation.

Yet another object of this invention is to provide an antenna designwhich reduces rf leakage to the other electronic components within thenose cone.

These and other objects and advantages of the invention will become moreapparent with reference to the following specification, drawings andappended claims.

SUMMARY OF THE INVENTION Briefly, in accordance with this invention, aprojectile is provided having a telemetry system which is built entirelyinto the nose cone structure. A dielectric material shaped to conform tothe nose cone of the projectile is adapted to be part of the exteriorwall of the projectile. The dielectrical material is provided with ametallic coating deposited so as to cover the entire inside surface ofthe nose cone and to extend so as to cover a portion of an outsidesurface. The tip of the dielectric nose cone structure remains exposedso as to define an open end dielectric loaded radiator. A slot shapedaperture is provided at the base of the nose cone in the form of anexposed portion of the dielectric material and this defines a slotteddielectric loaded cavity. A plurality of metallic coated holes locatedin the metallic coated portion of the nose cone and circumferentiallydisposed around the nose cone provide an electrical separation betweenthe open end dielectric loaded radiator and the slotted dielectricloaded cavity.

BRIEF DESCRIPTION OF THE DRAWINGS The specific nature of the invention,as well as other objects, aspects, uses and advantages thereof, willclearly appear from the following description and from the accompanyingdrawings in which:

FIG. 1 is a perspective view of the nose cone of a projectile inaccordance with this invention;

FIG. 2 illustrates an inside view of the nose cone of FIG. 1.

FIG. 3 illustrates the radiation patterns of the open ended cavitysection of the antenna in accordance with the present invention; and

FIG. 4 illustrates the radiation patterns of a single cavity inaccordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, nosecone 10 consists of a dielectric material such as epoxy fiberglas 12.The dielectric material is provided with a metallic coating 13 whichcovers the entire inside of the nose cone and extends over the edge 14and onto the exterior surface 11 of the nose cone. This coating istypically in the form of a copper plated surface which is coated on thedielectric material by means of a conventional electroless platingtechnique.

The base portion of nose cone 10 is provided with two radiating slots 15and 16 which constitute a dual dielectric loaded cavity witihcircumferential radiating slots. These slots simply constitute etched orexposed portions of the dielectric material 12. Each section of the dualcavity has its maximum radiating field normal to the axis of the coneand is fed from a coaxially input connector 21 and 22. If desired, bothcavities can be fed from a common source and phased in such a manner asto get maximum radiation off the side or along the axis of the cone.Associated with each coaxially input feed is a shorting post 18 and 19.This shorting post extends through the dielectric material and connectsthe outer conductive coating 11 with the inner conductive coating 13.The two shorting posts thereby distinguish and define the two separateslotted dielectric loaded cavities.

At the forward end or apex of nose cone 10 is the open ended dielectriccavity which radiates surface waves through the exposed dielectric 12into free space. This portion of the antenna has its maximum radiationnormal to the axis of the nose cone, with nodes along the axis. Again acoaxially input feed 26 (see FIG. 2) is provided in the upper half ofthe nose cone and associated therewith a shorting post 20 is locateddiametrically opposed thereto.

A plurality of closely spaced copper plated holes 17 are disposedcircumferentially in the plated portion of the nose cone. These closelyspaced holes form a conducting barrier which electrically separates theopen end dielectric loaded radiator located at the tip of the nose conefrom the dual slotted dielectric loaded cavity located at the base ofthe nose cone. Of course, it is possible to replace the plurality ofclosely spaced holes with a single exposed ring or slot of dielectricmaterial.

The typical nose cone size of the present invention is 3 inches highwith a 2 inch base diameter. The dielectric materials from which thenose cone is made have a wall thickness of approximatelythree-sixteenths inch and a dielectric constant of about 4. The antennahas a low input impedance, about a 5 percent bandwidth where the VSWR is2.0, and operates in the low S-band region. The radiation pattern ofthis portion of the antenna is shown in FIG. 3. The radiation pattern ofone section of the dual cavity antenna, located at the base of the cone,is illustrated in FIG. 4. These radiation patterns and measurements weretaken with the antenna assembly mounted on a cyclindrical bodystructure. It is, of course, possible to have other designs of thismulti-frequency antenna. For example, the dual cavity could be a singlecavity, designed to operate at a much lower frequency. Also, there aremany choices of dielectric materials which can be used that would changethe operating frequency and vary the performance. Other designsutilizing a ridge incorporated in the cavity will change the frequencyand bandwidth as desired. The conductive coating can be made out ofcopper, gold, silver, steel or platinum. The dielectric materials cantypically be made out of epoxy fiberglass, teflon, plastic or ceramic.

It will be appreciated that the antenna described herein eliminates manyof the problems and difficulties that plagued prior art systems. Amulti-frequency operating antenna system has been designed which is of aone piece integrated construction, is rigidly small and is provided withgood electrical isolation. Because the dielectric material is fullyplated on the inside, rf leakage to other circuits and components ismaterially reduced. The system requires no additional space and permitsthe inside of the nose cone to be utilized for other purposes.

It should be understood that the invention is not limited to the exactdetails of construction shown and described herein, for obviousmodifications will occur to persons skilled in the art.

I claim as my invention:

1. In the projectile of the class wherein a signal is generated within aprojectile to be transmitted from an antenna, the improvementcomprising:

a. a dielectric material shaped to conform to the nose cone of saidprojectile and adapted to be part of its exterior wall structure;

b. a metallic coating deposited on the inside surface of said dielectricand extending to cover a portion of the outside surface so as to leavethe tip of said nose cone exposed to define an open end dielectricloaded radiator;

c. a slot shaped aperture in said coating located at the base of saidnose cone to expose a portion of said dielectric and thereby define aslotted dielectric loaded cavity; and

d. a plurality of metallic coated holes in the metallic coated portionof said nose cone circumferentially disposed to electrically separatethe open end dielectric loaded radiator from the slotted dielectricloaded cavity.

2. The invention defined in claim 1 further comprising means forconnecting an input signal to said open end dielectric loaded radiator,and means for connecting a separate input signal to said slotteddielectric loaded cavity.

3. The invention defined in claim 2 further comprising a second slotshaped aperture to define a second slotted dielectric loaded cavity, andmeans for connecting an input signal thereto.

4. The invention defined in claim 3 further comprising a metallic coatedshort circuit hole associated with each of said means for connecting aninput signal.

1. In the projectile of the class wherein a signal is generated within a projectile to be transmitted from an antenna, the improvement comprising: a. a dielectric material shaped to conform to the nose cone of said projectile and adapted to be part of its exterior wall structure; b. a metallic coating deposited on the inside surface of said dielectric and extending to cover a portion of the outside surface so as to leave the tip of said nose cone exposed to define an open end dielectric loaded radiator; c. a slot shaped aperture in said coating located at the base of said nose cone to expose a portion of said dielectric and thereby define a slotted dielectric loaded cavity; and d. a plurality of metallic coated holes in the metallic coated portion of said nose cone circumferentially disposed to electrically separate the open end dielectric loaded radiator from the slotted dielectric loaded cavity.
 2. The invention defined in claim 1 further Comprising means for connecting an input signal to said open end dielectric loaded radiator, and means for connecting a separate input signal to said slotted dielectric loaded cavity.
 3. The invention defined in claim 2 further comprising a second slot shaped aperture to define a second slotted dielectric loaded cavity, and means for connecting an input signal thereto.
 4. The invention defined in claim 3 further comprising a metallic coated short circuit hole associated with each of said means for connecting an input signal. 